1. Field of the Invention
This invention relates generally to a high pressure discharge lamp employing a glow starter.
2. Description of the Prior Art
A high pressure discharge lamp such as metal-halide lamp and a high pressure sodium lamp have been used for their high output and high lighting efficiency. But presently such lamps need a special starting means because they have a high starting voltage.
So a high pressure discharge lamp using a glow starter having a glass body as a starting means has been developed. For example, U.S. Pat. Nos. 4,117,370 and 4,144,475 disclose using a glow starter as a starting means.
But the above mentioned glow starter is used as it is, i.e. without a covering for the body of the glow starter. Consequently, such a glow starter is apt to be deformed on account of heat radiation of the discharge tube for long periods of continuous lighting. A disadvantage of the conventional glow starter is its short life on account of impurity gases released therein as produced by heat radiation from the discharge tube. Moreover, the glow starter is mounted by means of welding of its leadwires to a support structure, so it may be damaged occasionally by a spark during welding. Further, since the glow starter is mounted solely by the welding of the leadwires, it is highly susceptible to damage from vibration or shock of the lamp.
A further problem attendant to the conventional lamp is related to the fact that the glow starter is fixed near the end of an outer bulb, and at times it is deformed by heat radiation of a gas burner during sealing of the outer envelope to the lamp stem member.